A thermoelectric module can convert a heat flow into an electric current by utilizing the so-called Seebeck effect. The Seebeck effect is based on an inversion of the Peltier effect. Such thermoelectric modules can therefore be used to recover heat or to generate electric energy from heat and can be correspondingly used in exhaust systems of internal combustion engines, preferably in motor vehicles, in order to improve the energy efficiency of the internal combustion engine or of the vehicle.
A thermoelectric module specifically comprises usually a plurality of leg pairs, which have each a p-doped semiconductor leg and an n-doped semiconductor leg, wherein the semiconductor legs are in contact with one another electrically via metal bridges. The leg pairs may hereinafter also be called LEG pairs. Conversion of thermal energy into electric energy takes place in every individual LEG pair. The plurality of LEG pairs are connected, furthermore, within the respective thermoelectric module, preferably in series, such that the respective thermoelectric module advantageously has only one positive pole and only one negative pole, at which the electric energy can be tapped. The LEG pairs may be connected especially via the metal bridges.
A thermoelectric module has, furthermore, a hot side and a cold side, at which the temperature difference is to be applied in order to generate a heat flow by the thermoelectric module, which said heat flow can be converted therein into electric current. The cold side and the hot side are usually formed on such a thermoelectric module by an electrically insulating ceramic plate, with which the metal bridges are flatly in contact (or have surface contact) and to which they are fastened.
To couple within a heat exchanger a heating tube, which carries a heating fluid, for example, exhaust gas of an exhaust system, as well as a cooling tube, which carries a cooling fluid, for example, a coolant of a cooling circuit, with the hot side and with the cold side, respectively, of such a thermoelectric generator or module in a heat-transferring manner, a prestress, which presses the respective tube against the thermoelectric module, is usually generated to improve the heat transfer.
Since the ceramic plates of the thermoelectric module have a high flexural rigidity and are comparatively brittle, close manufacturing tolerances must be maintained in order to avoid pressure peaks and hence force peaks at the ceramic plates. The effort needed for this during the manufacture of the heat exchangers is comparatively great.